I love Opera but it's never supported SpeedDownload and 1Password, my mandatory add-ons. I was messing with Opera looking to disable the built-in torrent client and saw "Download Manager" so I entered my path and .app name for SpeedDownload then went and downloaded a file. SpeedDownload actually intercepted the file and downloaded it...here's what I did:
1. In the Opera URL Bar type: OPERA:CONFIG
2. In gthe quick search bar type: DOWNLOAD MANAGER
3. In the text entry block type: /Applications/Speed Download 5/Speed Download.app (or whatever the path and name of SpeedDownload is)